JP6252182B2 - Manganese oxide reduction method in converter - Google Patents

Description

  The present invention relates to a manganese-containing molten steel production technique in which in a converter operation for producing molten steel from hot metal, both decarburization reaction by oxygen blowing and reduction reaction of manganese oxide by carbon in molten iron are performed in a single treatment. .

  Manganese components in steel are useful elements added to improve the toughness of steel and prevent segregation of slabs. Many manganese-containing steels are secondarily refined from manganese metal such as ferromanganese and metallic manganese. It is manufactured through a casting and rolling process after the ingredients are adjusted in the ladle process.

Since these manganeses exist as oxides such as manganese ore as natural resources, the purchase price of metal manganese for alloys is much higher than that of manganese ore.
Therefore, as described in detail in Non-Patent Document 1, manganese oxide can be carbon-reduced at the molten iron temperature during converter blowing, so that an inexpensive manganese ore is added to the converter and blown. Operations are being carried out to reduce the amount of manganese metal used in secondary refining by reducing it into manganese-containing molten steel.

  In addition, as described in detail in Non-Patent Document 2, the naturally produced manganese ore has a melting point of about 1550 ° C., so that a low melting point product (for example, a sintered product) is added and the converter is blown quickly. Research is being carried out to increase the reduction efficiency by making the hatched state with good reactivity at the time (low temperature range).

  Furthermore, since the manganese reduction reaction by carbon in steel is an endothermic reaction, it is well known that the reduction proceeds more favorably at higher temperatures, and the decarburized and refined high-temperature molten steel is stirred without oxygen top blowing. Means for proceeding the reduction reaction (Patent Document 1), means for producing a high Mn hot metal by maintaining carbon reduction at a high temperature for a long time (Patent Document 2), and the like have been proposed.

Yoshiaki Tabata et al .: Iron and Steel, Vol.76 (1990), p1916. Toshiyuki Kaneko et al .: Iron and Steel, Vol. 79 (1993), p941. Nikkan Kogyo Shimbun: Recommended equilibrium value of steelmaking reaction (1968). Satoshi Uchida et al .: Iron and Steel, Vol. 77 (1991), p490.

JP 2000-096117 A JP-A-61-272345

However, the results obtained in the operation described in Non-Patent Document 1 show that the manganese concentration obtained at 1630-1670 ° C is less than 1 wt% as shown in Fig. 8 on page 1920 of the same document. (0.6 to 0.9 wt%) molten steel is obtained, and even with the technique described in Non-Patent Document 2, even if a sintered product is used, a reduction improvement effect is recognized from the addition of manganese ore alone, As described in Fig. 16 on page 947 of the same document, the manganese concentration in the obtained steel was 0.8 wt% or less.
In general, the manganese content in products required for thick plates is often 1 to 3% by mass (may be described as mass%), and the demand for technology that can reduce more manganese ore is extremely high. Is.

Furthermore, in the means described in Patent Document 1 for favorably proceeding the manganese reduction in a high temperature range, the reduction time is extended by rinsing in order to carry out the manganese reduction, but as shown in FIG. The temperature at the start of rinsing is 1680 ° C or higher, and operation at such a temperature is severely worn for the converter refractory, leading to an extreme decrease in the refractory life or non-blowing. It included a serious problem that the frequency of furnace replacement performed during smelting increased and high productivity could not be maintained.
In addition, in order to reduce manganese ore in large quantities, there is a smelting reduction technique in which sufficient carbon concentration is ensured at a high temperature and long-time blowing is performed, as in Patent Document 2, which is obtained at this time. Since molten iron contains about 7% carbon, it cannot be made into a product in the secondary refining process.

  The present invention is based on the above-mentioned problems of the prior art, during a converter operation for producing molten steel from hot metal, when performing manganese oxide reduction, a large amount of manganese can be reduced, and a high temperature state that affects the refractory life The purpose is to provide an efficient operation method that does not expose to

  The inventors of the present invention have intensively studied a method for solving the above-described problems. As a result, the inventors have found a means by which inexpensive manganese oxide such as manganese ore can be effectively reduced and added by converter blowing. The summary is as follows.

(1) In a decarburization process of a converter for producing molten steel from hot metal having a carbon concentration of 2.5% by mass or more and a temperature of 1400 ° C. or less, a manganese oxide-containing additive is added to the molten iron, and the carbon concentration is set to 0.1%. When the molten iron temperature is 1% by mass or more and the temperature is 1500 ° C. or higher and lower than 1650 ° C., the acid feeding rate is decreased from the average acid feeding rate during the decarburization treatment, and the reduced time is set to 1 minute or more in total. A method for reducing manganese oxide in a converter, wherein the temperature is less than 1650 ° C.
(2) The converter belonging to (1) above, wherein the acid feed rate is 0 to 100 Nm ³ / h · t when the acid feed rate is lower than the average acid feed rate during the decarburization treatment. Manganese oxide reduction method.
(3) The manganese oxide reduction method in a converter belonging to (1) or (2) above, wherein a manganese oxide-containing additive is added to the molten iron until the molten iron temperature reaches 1450 ° C.
(4) The manganese concentration contained in the furnace slag as manganese oxide is 20% by mass or more when the acid feed rate is lower than the average acid feed rate during the decarburization treatment. A method for reducing manganese oxide in a converter belonging to any one of 1), (2), and (3).

  According to the present invention, inexpensive manganese oxide such as manganese ore can be effectively reduced and added by converter blowing, and its industrial utility value is extremely high.

It is a figure which shows typically implementation of this invention by an upper bottom blow converter.

  An embodiment of a method for reducing and adding manganese oxide in a converter of the present invention (hereinafter referred to as “method of the present invention”) will be described with reference to FIG. In addition, this invention method is not restricted to embodiment shown here, It can implement suitably with various converter type | mold refining facilities, such as a top blow converter, Q-BOP, and AOD.

  Molten iron 1 and slag 2 are inserted into the converter, and oxygen 4 is supplied from an upper blowing lance 3. A stirring gas 6 (nitrogen, carbon dioxide, oxygen, argon, or the like is appropriately used as the stirring gas) is blown from the bottom blowing tuyere 5. The converter is composed of an iron skin 8 lined with a refractory 7 (such as magnesia carbon as appropriate). A secondary material 10 is added from the hopper 9 into the furnace through the furnace port. The sub lance 11 has temperature measurement, sampling (metal and / or slag), and CD sensor (online batch [C] measurement based on metal freezing point measurement) functions.

In the decarburization process for producing molten steel from molten iron by a converter, in a general converter, the amount of molten iron corresponding to the furnace volume (furnace capacity ratio: volume in the furnace / volume of molten iron = about 5 to 9) is inserted, At present, due to the introduction of technologies such as the adoption of porous lances, the average acid feed rate per 1 ton of molten iron is 200 to 300 Nm ³ / h, and the blowing time until decarburization to molten steel of the specified component is 10 to 20 Minutes are common.

Here, the hot metal before decarburization includes not only hot metal discharged from the blast furnace (generally carbon concentration in molten iron: [C] ≥ 4 mass%), but also a carbon concentration lowered by hot metal pretreatment and lapping. Is also a target.
The definition of hot metal and molten steel is generally classified by [C], and the concentration varies depending on the literature. In the description of the present invention, in order to distinguish between high carbon concentration that does not require decarburization blown used for cast iron and the like, and high carbon steel that requires decarburization blown used for bearing materials and the like, [C ]> 2 mass% molten iron is treated as molten iron, and [C] ≦ 2 mass% molten iron is treated as molten steel.
In addition, since the present invention can be applied not only to general low alloy steels but also to the production of special high Ni products containing alloy components other than 20 mass% of iron, the molten iron contains 50 mass% or more of iron. Specified as molten metal.

  In the present invention, for the hot metal having a carbon concentration of 2.5 mass% or more and a temperature of 1400 ° C. or less, the carbon concentration of the hot metal before decarburization blowing in the converter for the purpose of producing molten steel from the hot metal In addition, the temperature is within this range, and in addition to being within the range suitable for the practice of the present invention, when the carbon concentration is less than 2.5%, ensuring the blowing temperature required from the next step onward. In addition, there is a shortage of carbon as a heat source for manganese reduction, which adds to the cost burden such as the addition of carbonaceous materials during blowing operation for reduction operation, and phosphorus distribution in high temperature hot metal Therefore, in hot metal with an initial temperature exceeding 1400 ° C, the hot metal [P] before processing often varies to a high level, and component removal due to high [P] for rephosphorization that proceeds simultaneously with manganese reduction, etc. This is because it is likely to cause operational troubles.

First, the current converter manganese reduction operation will be described.
The manganese reduction reaction into the steel being blown typically proceeds according to the following formula (1).
(MnO) + C → Mn + CO ↑ (1)
However, (MnO): MnO in the slag, C , Mn : C , Mn in the metal.

  For this reason, a MnO source is required to reduce and add manganese to the steel. As the MnO source, carry-over slag of precharge containing manganese oxide such as MnO can be used, but since the reduction amount is limited, manganese oxide-containing materials such as manganese ore are added and supplied from the hopper to the furnace By doing so, an effective manganese reduction operation can be carried out. At this time, manganese oxide may be added to the furnace with powder from the top blowing lance or bottom blowing tuyere together with the carrier gas.

The equilibrium constant K for manganese reduction in the above formula (1) can be uniquely defined as a function of the temperature T from known thermodynamic data as described in Non-Patent Document 3, for example.
That is, since the standard free energy change (ΔG °) in the equation (1) is expressed by the following equation (2), the equilibrium constant K for manganese reduction is as shown in the following equation (3).
MnO + C → Mn + CO (g) (1)
△ G ° = + 266020−167.64T (2)
K = (a _Mn · P _CO ) / (a _MnO · a _C ) = exp (−31997 / T−20.164) (3)
Here, T is the hot metal _{temperature, P CO} CO partial pressure of the _{furnace, a Mn} is Mn activity in the _{slag, a MnO} manganese oxide (MnO) activity in the slag, _{a C} is C activity in the slag Amount.

Therefore, in order to increase the manganese concentration in the molten steel (which is approximately proportional to a _Mn ), a constant temperature, that is, K is constant,
1) to ensure the manganese oxide concentration in the slag: ensuring the carbon concentration of maintaining 2) in the molten steel of a high a _MnO: it is important to two points the maintenance of high a _c, 1) for, Resusuragu blowing As for the operation of adding Mn ore at 2), the fact that it is important to ensure [C] ≧ 0.1 mass% is also described in Non-Patent Documents 1 and 2 mentioned above.

Here, in the converter operated at atmospheric pressure, if Pco ≧ 1 atm, the CO mass transfer on the gas phase side proceeds rapidly without being influenced by the atmospheric gas concentration until the equilibrium a _Mn is reached. The engineer can easily consider this, and as a means for that purpose, as described in Patent Documents 1 and 2, an operation has been directed to increase the K value by increasing the furnace temperature.

  Based on the above knowledge, the current converter manganese reduction operation is performed, but in order to carry out a large amount of manganese reduction, which is the above-mentioned problem to be solved, the converter operation is extremely hindered. It is required to carry out treatment at a high temperature of ℃ or higher for a long time, and the inventors have extended the temperature and operation time so that the decarburization and manganese oxide reduction reaction in the converter does not damage the furnace body. In order to establish an operation technology that does not become a problem, intensive research was conducted.

The most important issue in this research was the accurate evaluation of _aMnO (manganese oxide activity in slag) in the formula (3). Although the MnO activity in the slag can be calculated by various model calculations, the existing calculation evaluation method uses parameters determined based on experimental values and models them for evaluation.
For example, as is apparent from Fig. 2 in Non-Patent Document 4, even a simple CaO-MnO binary _aMnO has a large difference between the model calculation and the actual measurement value. Here, this experimental temperature is also a result of 1400 ° C., which is lower than the steelmaking temperature. Further, it has been confirmed that manganese oxide present in the manganese ore is mainly composed of MnO _2. There is a big problem that the exact ionic behavior of manganese, which is a transition metal in which valence and divalence are mixed, has not been clarified.

Therefore, the inventors investigated in detail the reduction behavior that occurs at the interface between various slag containing manganese oxide (slag that has been changed to various compositions by combining manganese ore or MnO reagent with converter slag, etc.) and molten iron containing carbon. did.
At that time, in the region where the carbon concentration in the steel is 0.1 to 3 mass%, various investigations of the manganese reduction rate and observation in the experimental furnace when the converter slag and manganese oxide coexist are carried out variously by the experimental furnace in the atmospheric pressure atmosphere, Under conditions exceeding 1500 ° C., it was clarified that boiling considered to be CO gas was generated from the slag metal interface and that the Mn reduction reaction proceeded very rapidly.

The CO gas boiling shows that has occurred, the CO mass transfer of the gas side is a critical condition which does not participate in the reaction rate for a state of greater than 1atm of equation (3) P _CO atmosphere . In particular, when the manganese content contained as manganese oxide in the slag exceeds 20 mass% (a value obtained by quantifying a sample obtained by pulverizing and magnetically selecting the slag and quantifying it with a fluorescent X-ray analysis method), the reduction reaction proceeds particularly rapidly. It was also confirmed that when the carbon concentration in the steel was less than 0.1 mass%, the reduction reaction was significantly stagnant.

  Therefore, in order to proceed the manganese reduction in the converter advantageously, the high temperature blowing temperature value of about 1650 ° C. as shown in the prior art does not have a great influence on the reduction rate. Can think. In converter operation at a constant acid feed rate, the temperature rises continuously, and the rate of rise varies depending on the temperature dependence of the dissipated heat and the oxidation reactants. Is well known from general operational experience. The effect of the present invention is not the effect due to such a temperature rise, but the effect that the blowing time from reaching the desired temperature of 1500 ° C. or higher, which has been clarified in this research, to the blowing stop is extended. It was supported by the following example of actual operation data analysis.

That is, under the condition of 70,000 Nm ³ / h of acid feeding in a 270 t / ch converter (total acid feeding time is 15 to 17 minutes), after the start of blowing, the blowing time from reaching 1500 ° C. until blowing is The 1630 ° C blowing (condition 1) is 4.3 minutes, while the 1680 ° C blowing (condition 2) is 6.0 minutes (28% extension). Comparing the amount of manganese reduction in condition 1 and condition 2, the increase in manganese reduction with respect to condition 1 in condition 2 is about 30%, and the rate of increase in reaction time at 1500 ° C or higher is almost equal to the rate of increase in manganese reduction. I found out.

  Based on the above findings, in order to efficiently carry out decarburization and manganese oxide reduction reaction in the converter, 1) high speed for quick decarburization and temperature rise up to 1500 ° C where manganese reduction rate is slow 2) In the region where the manganese reduction rate is higher than 1500 ° C, the oxygen reduction rate is reduced to ensure a long reduction time, and the carbon concentration is reduced and the converter blow-off temperature is reduced. It has been found that by completing the blowing in a temperature range where the refractory damage is small, it is possible to enjoy good reduction characteristics without extending wasteful treatment time.

Here, as a condition for reducing the acid delivery rate, as described above, the reducing power by carbon is extremely reduced [C]: If the carbon concentration is not higher than 0.1 mass%, the manganese reduction may proceed. In addition, even if the acid feed rate is reduced at a temperature of 1650 ° C or higher, the temperature of 1650 ° C itself is a range that causes great damage to converter bricks such as magcarbon. [C]: 0.1 mass% Above and below 1650 ° C were established.
The blowing temperature is also set to less than 1650 ° C so as not to damage the converter bricks.
Moreover, the condition for reducing the acid delivery rate to 1500 ° C. or higher is that, as described above, the condition of 1500 ° C. or higher is extremely desirable as the temperature for promoting manganese reduction, and the acid delivery rate is reduced at less than 1500 ° C. This is because the blowing time becomes longer and the productivity is lowered.

In conventional decarburization blowing, the acid delivery rate is high except for some purposes such as avoiding slopping, temporarily reducing the acid delivery rate for stable measurement during sublance measurement, and avoiding iron oxidation loss. Operation to maintain is performed. Therefore, the reduction reaction progresses in an extremely advantageous manner within 10 to 20 minutes from the start of the current high-speed blowing to the end of the blowing [C] ≧ 0.1 mass% and the molten iron temperature is 1500 ° C. or higher. Is a limited time of about 30% of the total blowing time, and the temperature and carbon concentration range where the good refractory damage described above is small and manganese reduction proceeds favorably are all blown. About 20-30% of the time.
On the other hand, in this invention, based on said acquired knowledge, an acid sending speed | rate is reduced during decarburization blowing and the time of favorable reduction conditions is extended intentionally. By intentionally extending the time of such good reduction conditions, the amount of manganese reduction that was difficult in conventional operations (molten steel with a manganese concentration of 1 mass% or more in molten steel without adverse effects such as refractory damage) Can be obtained.
Here, the average acid feed rate is defined by the following equation (4).
Average acid feed rate (Nm ³ / h · t) ＝
Blowing start to finish furnace injection O ₂ amount (Nm ³ ) / (Amount of molten iron (t) × acid sending time (min) / 60) (4)

In addition, when extending the reduction time in a good state by lowering the acid delivery rate from the average acid delivery rate, if the reduced time is less than 1 minute in total, it is more advantageous than conventional operation. Since a sufficient Mn reduction rate could not be obtained, the maintenance of 1 minute or more was defined as a necessary condition.
As will be described later, in order to obtain steel with a remarkable economic effect of [Mn] 2 mass% or more by reduction operation in a converter, it is possible to reduce the acid supply by 2 minutes or more, based on the findings of the inventors' experiments. It has also become clear that it can be implemented in operation.

  The upper limit of the maintenance time for obtaining an advantageous Mn reduction rate according to the present invention is not specified. What is necessary is just to perform within the range which can ensure economical advantage. For example, for high Mn addition at 3 mass% level, reduce the acid feed rate, and add carbonaceous material to maintain [C] (0.1 mass% or more) necessary for manganese reduction and decarburization. Blowing extension operation can be carried out, but when the extension time exceeds 60 minutes, the disadvantage of the reduction in productivity of the converter for the purpose of decarburization is described as described in Patent Document 2. It is expected that the economic benefits compared to using a manganese reduction furnace cannot be said to be winning.

The amount of acid delivered after the average acid delivery rate has fallen below the upper limit is desirably 100 Nm ³ / h · t or less. This means that the average acid feed rate in current converters in Japan and overseas can be seen in the range of 200 to 270 Nm ³ / h in the above 270 t / ch converter (260 Nm ³ / h · t). It is 300Nm ³ / h · t, and it is very suitable for efficient Mn reduction operation by reducing the decarburization rate and temperature rise rate by setting the acid feed rate to 100Nm ³ / h · t or less. Because. The lower limit includes 0 Nm ³ / h · t. This is because the effect of the present invention is obtained when conditions such as a short-term rinsing are less affected by a temperature drop, or when an excessive temperature operation that requires the addition of a coolant is expected for dynamic control or the like. It is because it is suitable for.

  In addition to the manganese oxide in the carry over slag from the previous charge, the addition method in the case of adding manganese oxide is as follows: before blowing, simultaneously with scrap, after completion of hot metal insertion or during blowing However, it takes about 2 minutes to heat the manganese oxide and surrounding slag temperature up to 1500 ° C where good reduction characteristics can be seen. In furnace blowing, it corresponds to the time for the molten steel temperature to rise by 50 ° C, so it is desirable to add manganese oxide in the region where the molten iron temperature is 1450 ° C or lower.

Furthermore, as has been clarified from the results of the above research and study, the manganese concentration contained as an oxide in the slag is 20 mass% or more, and particularly good reduction characteristics can be obtained. When changing to 100 Nm ³ / h · t, the manganese concentration contained in the furnace slag as manganese oxide is preferably 20 mass% or more. The manganese concentration can be selected and confirmed as appropriate based on the measurement results, for example, by collecting the slag at the timing of changing the acid delivery with a sublance during blowing, magnetically selecting it, and measuring it with fluorescent X-ray analysis. is there.

  Next, the present invention will be further described based on examples, but the conditions in the examples are one example of conditions adopted for confirming the feasibility and effects of the present invention. It is not limited to the example conditions. The present invention can adopt various conditions as long as the object of the present invention is achieved without departing from the gist of the present invention.

The experimental basic operation of the example uses an upper-bottom blowing converter with a capacity of 270 tons, blasting hot metal with an initial temperature of 1240-1300 ° C and [C] of 3.7-4.1%, unavoidable impurities (mass%) [Si] <0.08, [Mn] <0.1, [P] <0.03, and [S] <0.01.
As a basic condition, manganese ore with Mn grade 47% as manganese oxide was blown by adding 14.3 t (reduction rate 100% △ [Mn] = 2.5 mass%) from the hopper. Therefore, a mixture of manganese ore and converter slag was also used. Also, for the purpose of changing the carbon concentration change level during processing, coke (for carburizing purposes) and iron ore (for reducing carbon concentration) are added as appropriate before the start of blowing and 2 minutes after the start of blowing. did.

The oxygen feed rate at the start of blowing is 70000 Nm ³ / h (260 Nm ³ / h · t). From the hot metal temperature at the beginning of feeding and the actual results of feeding, and the sublance measurement, [C] and molten iron during blowing The temperature was estimated, and the acid feed rate was changed at the target of the experimental level. Immediately after blowing, the temperature was measured with a sub lance, and the temperature after blowing and the components (metal, slag) were comparatively evaluated by sampling.
Note that the above-mentioned acid feed rate (70000 Nm ³ / h) at the start of blowing is the average acid feed rate defined by the above equation (4).

Characteristic of the present invention, in a state where the acid delivery rate is reduced from the average acid delivery rate, and [C] ≧ 0.1 mass%, the time under appropriate conditions of 1500 ° C. to less than 1650 ° C. Time) was determined by [C] using the dynamic control system obtained from the operating conditions such as the sublance measurement and the amount of acid delivered, and the temperature continuous calculation model indicated value.
Preliminary tests comparing the sublance measurement value ([C], temperature) between two points and the dynamic control indication value confirmed that the measurement error of the appropriate condition time after the decrease in the acid delivery rate by this method was less than 10 seconds. ing.

The experimental results are shown in Table 1.
Inventions 1 and 2 add manganese ore before the start of blowing (flow rate change after changing the acid feed), and Invention 3 is added during blowing (added at a metal temperature of 1420 ° C), both of which are 2 mass%. Blow [Mn] results exceeding 1, were obtained and good.
The present invention 4 has an acid flow rate of 30000 Nm ³ / h (111 Nm ³ / h · t) after changing the acid feed, and good reduction characteristics were confirmed in substantially the same manner as in the first invention.
The present invention 5 is the one in which the addition of manganese ore was performed when the molten iron temperature was 1463 ° C. after the start of blowing, but the slag was collected by sublance when the acid feed rate was changed (structure to adhere and collect on the metal plate provided on the outer periphery of the probe). Adhesive slag could not be collected. This is thought to be because slag solidification occurred due to the addition of manganese ore from the addition of manganese ore to the change in the acid feed rate, and it was not possible to collect it, and the blowing [Mn] was 1.5 mass%, which is more than the present inventions 1 to 3. It was low.

Invention 6 is a mixture of manganese ore and converter slag (2: 1) added, but the manganese concentration in the slag when the acid feed rate was reduced was 15.8 mass%, and the reducing power was reduced. Manganese reduction rate was low.
In the present invention 7, the decrease in the acid delivery rate is set to 40000 Nm ³ / h (148 Nm ³ / h · t), and a desirable reduction time is secured for 1.5 minutes, but the time from the decrease in the acid delivery rate to the blowing is somewhat short. The reduction rate was slightly lower and the blown Mn was 1.4 mass%.

In Comparative Example 1, manganese ore was introduced and operated at the same acid feed rate (70000Nm ³ / h constant) as in normal decarburization blowing, but the blowing stop [Mn] was as low as 0.8 mass%. there were.
In Comparative Example 2, the timing of decreasing the acid delivery rate was changed at 1410 ° C under almost the same conditions as in the present invention 1, but the blowing time was extended, but at a critical temperature of 1500 ° C or lower. Since the time was extended, the blown stop [Mn] was not significantly different from that of the present invention 1, and the production time was insufficient due to the processing time extension in the secondary refining process.
Comparative Example 3 is the operation data in which the appropriate time after changing the acid feed is less than the specified time, but the appropriate time is 0.9 minutes and less than the specified 1 minute. There was no significant difference in rates.

In Comparative Example 4, the timing for changing the acid supply was set to 1655 ° C. Manganese reduction was good, but the blowing temperature was 1688 ° C, and the slag line of the converter was severely damaged, and the next charge It was necessary to delay the treatment and carry out repairing work for the thermal spraying furnace, which hindered production.
Although the comparative example 5 was the result of having implemented carbon concentration at the time of a change of acid delivery with 0.08 mass%, blowing stop [Mn] was insufficient with 0.2 mass% by carbon shortage.

  As described above, according to the present invention, it is important to improve the characteristics of steel products. Manganese, which is important for improving the properties of steel products, is reduced in carbon during the converter smelting of manganese oxide. Therefore, high-order [Mn] molten steel can be produced, it is economical and easy to operate, has extremely high industrial value, and is highly usable in the steel industry.

DESCRIPTION OF SYMBOLS 1 Molten iron 2 Slag 3 Top blowing lance 4 Oxygen 5 Bottom blowing tuyere 6 Stirring gas 7 Refractory 8 Iron skin 9 Hopper 10 Secondary material 11 Sublance

Claims (4)

In the decarburization process of a converter for producing molten steel from hot metal having a carbon concentration of 2.5% by mass or more and a temperature of 1400 ° C. or less, a manganese oxide-containing additive is added to the molten iron, and the carbon concentration is 0.1% by mass. As described above, at a time when the molten iron temperature is 1500 ° C. or more and less than 1650 ° C., the acid feed rate is decreased from the average acid feed rate during the decarburization treatment, and the reduced time is set to 1 minute or more in total, and the blowing temperature is set to 1650 A method for reducing manganese oxide in a converter, characterized by being less than ° C.
2. The manganese oxide in the converter according to claim 1, wherein the acid feed rate is 0 to 100 Nm ³ / h · t when the acid feed rate is lower than the average acid feed rate during the decarburization treatment. Reduction method.
The method for reducing manganese oxide in a converter according to claim 1 or 2, wherein a manganese oxide-containing additive is added to the molten iron until the molten iron temperature reaches 1450 ° C.
  The manganese concentration contained as manganese oxide in the slag in the furnace when the acid feed rate is reduced below the average acid feed rate during the decarburization treatment is 20% by mass or more. The method for reducing manganese oxide in a converter according to any one of the above.

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